BIOL 112 1st Edition Lecture 13 Outline of Last Lecture I Chloroplasts A Second Endosymbiosis II Modern Protistans III Traditional Groupings IV General Eukaryotic Life Cycle V Terms VI Domain Eukarya VII Supergroup Excavata VIII Alveolata IX Apicomplexans X Stamenopila XI Oomycota XII Supergroup Archaeplastida XIII Animals XIV Body Plan Criteria for Organizing Animals XV Digestive System Outline of Current Lecture XVI Phylogenetic Trees XVII Early Animal Evolution XVIII Vendian Animal Fossils XIX The Cambrian Explosion XX What happened These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute XXI Hox Gene Clusters XXII Patterning Genes XXIII Phylum Chordata XXIV Disagreement of Schemes Current Lecture I Phylogenetic Trees Suggested evolutionary patterns depending on the sources of information used to construct the criteria for the branch points Body plan morphology and development embryology based scheme Molecular sequence based scheme Schemes produced are different in some details Agreement of Schemes All animals have a common ancestor Sponges are barely multicellular extremely primitive animals Eumetazoa all animals except sponges have true tissues Most animals are Bilateral bilateral symmetry Vertebrates and a few other phyla belong to the deuterostomes Most invertebrates belong to the protostomes II Early Animal Evolution How did we get animals Have to use molecular data to figure this out First eukaryotic like fossils 2x10 9 years ago Proterozoic Possible animal ancestors are choanoflagellates protists that resemble cells of sponges Earliest animal like forms 640x10 6 years ago Ediacaran III Vendian Animal Fossils 635 x 10 6 551 x 10 6 years ago Includes the Ediacaran formations from Australia but similar age fossil beds were found in China and the North Sea region Fossils are very difficult to interpret What kinds of animals Unusual morphologies Body plans Bilateral symmetry not obviously apparent Organs Appendages Any descendants in modern times Fossils uncommon all soft bodied Some recognizable as cnidarians and perhaps ctenophores Most are unlike any modern forms Some are quite large up to 2 meters long Many Vendian animals have a quilted appearance multiple thin extensions connected along a central axis Others seem to have lived on a stalk and might have had triple symmetry like Charniodiscus All disappear about 551 x 10 6 years ago Geological evidence of a planet wide ice age then environmental catastrophe that would cause extinctions IV The Cambrian Explosion Beginning about 550 x 10 6 years ago appearance of most modern animal phyla over 10x10 6 year period Pre Cambrian animal fossils are difficult to interpret in modern terms Ediacaran Period 680x10 6 550x10 6 animal fossils are flattened and without shells or skeletons At Cambrian Explosion fossil animals become common because we now see shells and skeletons things more easily preserved Transition to Cambrian Forms It appears that most Vendian animals became extinct and left no modern descendants Cambrian forms more modern in appearance distinct A P and d v axes and with hard parts shells But what was transition from primitive body plan radially symmetrical to bilateral symmetry What lineage What genes involved V What happened Animal phyla have developed ability to make shells and skeletons Cephalization bilateral symmetry Predator prey arms race armor Increasing O2 in atmosphere made higher metabolisms bigger bodies possible Development of effective circulatory gas exchange systems so that a thicker body is possible Molecular basis animals evolved regulatory gene combinations Homeobox Hox Cluster on one arm of chromosome distinguishing feature of being an animal to build basic animal body plan bilateral symmetry A P and d v axes with limbs cephalization in larval and adult forms Ancestral Bilateral General agreement that common ancestor to modern bilaterian phyla is most likely something like a flatworm Has bilateral symmetry A P and d v axes Bilateral symmetry implies cephalization development of a head brain cluster of sensory organs on anterior Three tissue layers formed by gastrulation But how get from more primitive phyla sponges cnidarians etc to the flatworm form Compare existing pre bilaterian forms to existing bilaterians to assess what might have happened to genetics Analysis of What Happened Fossils are limited Can examine existing pre lateral phyla basal taxa for possible ancestral genetic content relative to axes formation and embryology VI Hox Gene Clusters Common patterns of expression in evolutionarily diverse organisms Significance to formation of A P axis in embryo homeobox cluster genes pattern out the embryo structures from anterior to posterior Pattern of genes on chromosome reflects A P pattern of expression of genes in embryo VII Patterning Genes A P Genes Homeobox and Related Genes Critical feature in K Animalia is Hox Cluster Regulatory genes control expression of other genes Expression of the genes on the chromosome is related to spatial expression in the embryo d v Genes Dpp Sog Chrd Bmp4 Expression defines dorsal and ventral sides of embryo Dpp Sog defines d v in flies Chrd Bmp4 defines d v in vertebrates Do basal groups have these genes Are they expressed in similar patterns in embryos Embryology The way the embryo develops is critical to how body plan develops in animal Gastrulation Folds embryo into 3 dimensions Begins formation of the digestive system Develops two or three layers of tissues in embryo germ layers Location and control of gastrulation critical to development VIII Phylum Chordata Vertebrates are sub phylum within this phylum Very old early chordates seen in Burgess Shale Distinguishing Characteristics of this Phylum Presence of a notochord at some time in life cycle Dorsal hollow nerve cord nervous system spinal cord Presence of pharyngeal slits at some time in development Presence of post anal tail IX Disagreement of Schemes Mostly in the bilateral groups Morphology Development based scheme divides bilaterians into two groups Deuterostomes Chordates and Echinoderms Protostomes Arthropods Molluscs and Annelids Molecular based scheme divide bilaterians into three groups Deuterostomes chordates echinoderms Lophotrochozoans annelids molluscs Ecdysozoans arthropods